The pick is reportedly a conditional fourth-rounder that could become a third- rounder based on the veteran receiver's on-field production.

The trade comes one day after the Bills moved up from the ninth overall pick to fourth in a trade with Cleveland to take Watkins in Thursday's first round of the NFL Draft. Buffalo sent its first and fourth round picks in 2015 in exchange for moving up five spots to take the record-breaking Clemson wideout.

The 6-foot-1 Watkins had 101 catches for 1,464 yards and 12 touchdowns in 13 games for Clemson this past season and ended his career with a slew of school receiving records.

The Bills acquired wide receiver Mike Williams in a trade with Tampa Bay last month. With the addition of Watkins, Johnson became the odd man out in Buffalo.

Johnson spent the past six seasons with the Bills, catching 301 passes for 3,832 yards and 28 touchdowns. He had three consecutive 1,000-yard seasons from 2010-2012.

"Stevie was a great contributor during his career with our organization," said Bills general manager Doug Whaley. "Today's decision was not an easy one to make, especially involving a player like Stevie who leaves everything he has on the field and is an emotional leader in our locker room. All of the decisions we make are done so in the best interest of our team. We wish him the best of luck in San Francisco and throughout the rest of his NFL career. We also want to thank Stevie and his family for their commitment to the Buffalo Bills and the community over the last six years."

The 27-year-old Johnson caught 52 passes for 597 yards and three scores over 12 games in 2013.

The Kentucky product was drafted by the Bills in the seventh round of the 2008 NFL Draft.